Computer printers such as ink jet printers often use different printing techniques for different types of printer media, such as conventional paper, specialized ink jet paper, coated paper, and transparencies. Depending of the media characteristics, different printing algorithms are used to prevent undesirable image characteristics such as color ink bleed, which varies with media type.
In addition, a given printer may be used for printing on different sizes of media. In such cases, it is helpful for the image printed to be sized to fit the media. This avoids images bleeding off the sheet edge, requiring two sheets, or failing to fill the full sheet area if desired. Also, dual sided or duplex printing requires careful manual reloading of the media supply during the printing process, with errors frequently occurring due to misorienting the media stack.
While paper size, type, and orientation may be properly established and manually entered into the printer memory or connected computer by an alert user, it is desirable to automate such tasks to simplify operation and to avoid likely errors. Existing media has been provided with bar coded identifying data for scanning by a printer. Such bar codes are typically provided at the corner margins of sheets on both sides, and are printed in a normally invisible fluorescent ink. The bar code ink fluoresces at an infrared wavelength in response to illumination by a red emitter in the printer, and is read by an optical scanner in the printer.
A typical printer drives paper along a feed axis, and has a print head carriage reciprocating over the paper along a perpendicular scan axis. In some printers, the bar code sensor is stationary, and mounted to the printer chassis at the edge of the paper path. Such fixed sensors may be readily shielded from exterior light, and may read a bar code as the paper is initially fed along the feed axis before the carriage begins to reciprocate. The lines of the bar code on the paper must be oriented perpendicular to the feed axis for use with a fixed sensor. In other printers, the sensor is mounted on the carriage, so that it may also perform other sensing functions such as media edge detection and ink color registration procedures. For carriage mounted sensors, the bar code lines on the media sheet must be oriented perpendicular to the scan axis. Bar coded media for one type of printer sensor is not necessarily compatible with the other type of sensor, requiring inventory of two media code types, and possible user confusion.
Transparencies present an additional challenge, as they are unsuitable for printing invisible bar codes. A paper strip may be attached to a margin of the film for printing indicia, but such a sheet will be limited for use only with a given type of printer sensor.
The present invention overcomes the limitations of the prior art by providing a bi-directionally scannable bar code pattern having a parallel array of alternating lines and spaces, each having selected widths. Each line has a common series of segments and segment spaces of selected lengths. The length of each segment may be the same as the width of a corresponding line, and the length of each segment space may be the same as the width of a corresponding space between lines. The pattern may be printed on a sheet of printer media, or on a strip attached to such a sheet.